In recent years, in an illumination light source of a luminaire, an incandescent lamp or a fluorescent lamp is being replaced with an energy-saving and long-lived light source, for example, a light-emitting diode (LED). Besides, a new illumination light source, for example, an electro-luminescence (EL), an organic light-emitting diode (OLED) or the like is also developed. Since the light output of the illumination light source depends on the value of flowing current, when illumination is lighted, a power supply circuit for supplying a constant current is required. Besides, in order to adjust an inputted power supply voltage to a rated voltage of the illumination light source such as the LED, the voltage is required to be converted. A switching power supply such as a chopper type DC-DC converter is known as a power supply having high efficiency and suitable for power saving and miniaturization. Besides, an LED lighting device using the switching power supply is proposed (see, for example, patent document 1).
[Patent document 1] JP A. 2004-119078
However, in the chopper type DC-DC converter, since current, flows through a diode having a large voltage drop when a switching element is off, there is a problem that a power loss is large.
Exemplary embodiments described herein provide a switching power supply having a small power loss and a luminaire.